There are a wide range of lifting/hoisting devices and configurations used to secure a ring or other clasping or coupling member to an object to be lifted (i.e. the “load”). Such hoisting devices include for example, center-pull and side-pull hoist ring assemblies. These hoist ring assemblies can be attached to a variety of heavy loads or objects, such as die sets and molds. The hoist ring assemblies usually include an integral load-carrying or load-lifting ring, clevis, bail, hook, loop, or similar clasping or coupling element. The load may be lifted with a lifting mechanism (e.g. a hoist), which can be connected to the coupling element of the hoist ring assembly in order to lift the object.
A large number of hoist ring assemblies have been developed that include a load-carrying ring, wherein the hoist ring assemblies, or parts thereof can pivot and/or swivel for the purpose of adjusting the orientation of the coupling element with respect to the force vector being applied to the coupling element during the lifting procedure. Various such hoist ring assemblies are found in patent documents discussed in more detail below, and which are incorporated herein by reference.
Center-pull hoist ring assemblies conventionally include a post assembly comprising a threaded bolt, a support member, and the load-carrying ring. The support member connects the ring to the post assembly. The threaded bolt of the post assembly engages a threaded opening in the load. The ring is used to attach the hoist ring assembly to the lifting mechanism. The support member, which carries the load-carrying ring, can swivel 360 degrees about a longitudinal axis of the bolt, thus allowing the ring to swivel to the same extent. Further, the support member often carries the ring such that the ring can pivot about a ring axis that is generally orthogonal to the longitudinal axis of the bolt. In this respect, the ring can have a pivot arc (i.e. “bail angle”) of about 180 degrees.
Like the center-pull style, conventional side-pull hoist ring assemblies include a rotating support member mounted by a post assembly onto the object to be lifted. In a side-pull hoist ring, the support member can be generally U-shaped to define an outer bite portion in the bottom of the U-shaped support member and in which a circular load bearing ring can be pivotally mounted. The circular load bearing ring is offset from the center axis of the post assembly.
Prior devices are those shown in Schron Jr. et al. U.S. Pat. No. 5,634,734 that discloses a center-pull style hoist device, which is incorporated herein by reference for showing the same. Also incorporated herein by reference are the devices shown in Ma U.S. Pat. No. 6,749,237, in Tsui U.S. Pat. Nos. 5,405,210 and 5,848,815, in Sawyer et al. U.S. Pat. No. 5,586,801, and in Chandler U.S. Pat. No. 5,352,056, which all show different styles of center-pull hoist ring assemblies.
Fuller et al U.S. Pat. No. 6,652,012; Fuller et al. U.S. Pat. No. 6,443,514; and Fuller et al U.S. Pat. No. 6,068,310 all disclose side-pull hoisting devices and are incorporated by reference for showing the same. All of these devices disclose hoist ring assemblies that have been used effectively in the industry for many years and which are provided as background for the invention of this application.
In addition to the above-described hoisting devices, also known in the patent art are patents to Mueller U.S. Pat. Nos. 5,286,130, and 3,492,033, which disclose clevis hoist ring assemblies. The Mueller patents are incorporated by reference for showing additional types of hoist ring assemblies that could be utilized in the invention of this application.
While hoist ring assemblies are designed to be very robust, every assembly has a predetermined load limit determined by the manufacturer, which is based on various factors including the size and design of the load-bearing ring. If a predetermined load limit of the assembly is exceeded, failure of the assembly can result. Such failure can include for example, the load-bearing ring being damaged. Conventionally, the bolt for the hoist ring assembly may be chosen to correspond to the load limit of the load bearing ring and/or to other components of the hoist ring assembly. Thus, hoist ring assemblies include a specific bolt of a particular size and rating.
The overall performance of the hoist ring assembly, the services life of the bolt, and the service life of the load bearing ring can depend on the proper tensile stress being exerted on the bolt from being threaded into the threaded opening of the object to be lifted. This tensile stress exerted on the bolt causes elongation of the bolt and is known as the “preload” or “designed tension” of the bolt.
In use, it is important to attach the bolt to the load to the proper preload in order to prevent fatigue failure of the joint, joint separation, or self-loosening of the bolt due to vibration. Therefore, bolts are configured to be tightened to a specific preload, which is the amount of tensile stress applied to the bolt during tightening that results in a fully tightened bolt without over tightening the bolt. When the preload is reached, the bolt is considered to be optimally tightened in a threaded opening. Attaining proper preload is important because when attained, the bolt does not carry the full weight of an applied load. Rather, only a percentage of the weight of the load is carried by the preloaded bolt. Conversely, when bolts are not preloaded, the full weight of an applied load is carried by the bolt.
The amount of torque (i.e. “tightening torque”) that is used to turn the bolt in the threaded opening has conventionally been measured and accepted as an approximation of the tensile stress on the bolt and used to determine whether the appropriate preload has been reached. While there are many tools available in the art to accurately test tightening torque applied to the bolt, torque is not the most precise measurement of tensile stress on the bolt because of variable friction factors between the bolt and the threaded opening of the load. Furthermore, such torque measurement tools are often cumbersome to use and taking the measurements take a considerable amount of time and effort, thereby reducing operational efficiencies.
Because of these deficiencies and/or because of the lack of proper measuring equipment, some end users do not properly conduct testing of tightening torque of the bolt. Additionally, tightening torque is conventionally only measured at a single time, namely, when the bolt is tightened in the opening of the object to be lifted. In this aspect, there is no way to assess whether or not the bolt is under adequate tensile stress at a time after the bolt is tightened into the threaded opening.
Therefore, there is a need for improvement in testing for the proper tensile stress on the bolt of a hoist ring assembly.